Coordinated activation and repression of genes are essential for the normal progress of the ovarian cycle. Ovarian granulosa cells express high levels of the transcription factors GATA-4 and GATA-6. In cell cultures, these transcription factors were shown to play key roles in the expression of enzymes involved in steroidogenesis. We have demonstrated in several recently published papers that GATA-4 is critical for the production of estradiol, which is essential for granulosa cell proliferation and follicle maturation. In addition, the finding that low expression of GATA-4 is associated with follicular cell death suggests that this factor also plays a survival role in the ovary. Because GATA-4 and GATA-6 null mice are embryonic lethal, the ultimate role of GATA in ovarian function remains unknown. This study is therefore designed to determine the physiological role of GATA-4 and GATA-6 in ovarian steroidogenesis, follicular development, and female fertility. The specific aims of this study are: 1- To generate ovarian-specific GATA-4 and GATA-6 null mice in order to find out the explicit roles of these transcription factors in the ovary in vivo. The Cre-lox technology will be used to delete part of the coding region of GATA-4, GATA-6, or their combination. We expect these mice to have severe defects in steroid production and in follicular development. 2- To determine the effect of GATA-4 and GATA-6 deletion on ovarian cells in vitro. Granulosa cells lacking GATA-4, GATA-6, or both will be used to examine the specific roles of these factors in steroidogenesis, cell proliferation, granulosa-cell hormone response, and gene expression. 3- To identify those genes that are regulated by GATA-4 and GATA-6 in fully functional ovaries in vivo, we will use ChIP-on-chip assays. All the results obtained to date indicate that GATA-4 and GATA-6 may play a crucial role in the normal function of the ovary. We expect from this investigation to clearly define the function of GATA-4 and GATA-6 in the steroidogenic capacity and growth of granulosa cells, to determine whether GATA-4 and GATA-6 have redundant effects on these cells, and to identify GATA-4 and GATA-6 target genes in the ovary. This study will not only provide critically important information on the regulatory mechanism underlying normal ovarian function but also may shed light on ovarian diseases due to improper granulosa cell function such as granulosa cell tumors and infertility.